SDH SONET 1

PDH SDH SONET.

SDH and SONET are transmission equipment. To understand their working, we need to discuss the PDH structure first.

PDH Plesiochronous Digital Hierarchy.

Plesio = Near Chronous = Time.

This system is nearly synchronized. Different Stages are almost synchronized. It was very famous Multiplexing technology.The basic data rate is 2.048Mbps for European standard E1. For North American standard T1 is 1.544Mbps.

PDH disadvantages

Plesiochronous Structure. Every apparatus has its own clock. Input tributary clock rate is slow than multiplexing equipments. No network level synchronisation.bit stuffing is used.

Restricted management. Low level tributary access require full system de-multiplex. No monitoring overhead. No management overhead. No NMS provisioning. No common standard among vendors. Only point to point communication. A complex cabling infrastructure between multiplexers. Big size. No standard optical interfaces.